The present invention relates to a system and method for program transmission optimization over a distribution system and relates particularly, though not exclusively, to a method and system for video transmission optimization.
Throughout the following specification the word xe2x80x9cprogramxe2x80x9d should be understood in the broadest sense of the term and includes any information, whether visual, tactile, olfactory, audible, or other information, a mixture of these or otherwise, which is normally perceived in a substantially continuous sequence of impressions through one or more of the human senses. The term xe2x80x9cvideo programxe2x80x9d refers to a program of visual information or visual and audible information, whether recorded in reproducible format or transmitted xe2x80x9clivexe2x80x9d. In our xe2x80x9cinformation societyxe2x80x9d, with its increasing -emphasis on greater accessibility to information, there are many situations where the same program may be required to be accessed by more than one person at the same time.
Thus, for example, in a library of a large educational institution which stores lectures and other information on audio and/or video cassettes, the demand for certain programs may be particularly high at certain times and there is a need to be able to allow several students to listen to or view the program simultaneously from the beginning, without having to force individuals to start listening to or viewing the program at the same time. Ideally, it should be possible to service the needs of all persons requiring that program immediately when it is requested. In practice this is extremely difficult without expensive duplication of equipment and complex electronic processing. Another example of this type of multiple user situation is so called video-on-demand television. A video-on-demand system ideally allows any subscriber to request (demand) any particular video program at any time of the day.
A prior art video-on-demand system is described in U.S. Pat. No. 4,506,387 to Walter in which each video program is pre-programmed in a memory device selectable by a host computer at a central data station in response to an address signal transmitted from the user. The host computer controls the transmission of the video program at a high non-real-time rate over a fibre optic line network to a data receiving station at the users location. The data receiving station then converts the received optical data to electrical data and stores it for subsequent real-time transmission to the users television set.
There are a number of significant disadvantages with the system of Walter, the foremost being that it is incompatible with existing television transmission networks, and in particular CATV coaxial cable networks. In order to achieve a rapid response time Walter transmits all of the digital data corresponding to an entire program to the receiving station over a plurality of fibre: optic lines within a very short time. Even with compression of the digital data the bandwidth requirement for this system is relatively large. For example, sixteen (16) optical data channels over four fibre optic lines are required to transmit a two hour movie in about thirty one seconds. Very few homes or buildings currently have ready access to a fibre optic cable, and a fibre optic network is expensive to install.
A further disadvantage with the system of Walter is that it cannot adequately handle a high demand for the same video program. Research in video tape lending libraries indicates that out of a total of say five thousand tapes held in the library, at any one time only a core group of twenty to forty most popular titles are in high demand. Furthermore, this research into the viewing habits of viewers indicates that the core video demand requirement varies throughout the day as the nature of the viewers changes. Walter contemplates that the central data station may transmit only a portion of the selected program to the user for his viewing, and then begin transmitting a portion of another selected program to a second user. A fixed multiplexing scheme, such as that of Walter, services each user""s request in turn with a high speed transmission burst which may be a portion or all of a program. It is forced to repeat that burst to start a second user at the beginning of the same program since there is an unvarying FIFO (first in first out) sequence to the program data and no redundancy. If a second user of the same program is physically on the same bus and is to be served before the burst is over the first user must be temporarily denied transmission. Clearly with core video programs this could result in unacceptable delays.
The present invention was developed with a view to providing a method and system for program transmission optimization over a distribution system for multiple users, and was developed specifically, though not exclusively, with a view to providing a system and method for supplying video-on-demand which is compatible with existing video distribution systems such as CATV. Throughout this specification the term xe2x80x9cdistribution systemxe2x80x9d is to be construed in the broadest sense of the term and covers ordinary radio and television networks, including satellite and microwave networks, CATV and internal television/video/audio distribution systems of the kind employed in hotels, educational institutions and more recently in aircraft and ocean liners.
According to one aspect of the present invention there is provided a method of transmitting a program to multiple users over a distribution system, the method comprising:
at a head end of the distribution system, providing a program divided into a plurality of segments; and
transmitting the segments from the head end to users"" receivers such that, at least some of the segments are transmitted more than once from the head end so as to enable multiple receivers of users requesting playback of the program at different times to simultaneously receive the segments required for continuous playback of the program.
According to another aspect of the present invention there is provided a system for transmitting a program to multiple users comprising:
means for providing a program divided into a plurality of segments at a head end; and
means for transmitting the segments from the head end to users"" receivers such that at least some of the segments are transmitted more than once so as to enable multiple receivers of users requesting the program at different times to simultaneously receive the segments required for continuous playback of the program.
According to a further aspect of the present invention there is provided a method of transmitting a program to multiple users over a distribution system, comprising:
at a head end of the distribution system, providing a program divided into a plurality of segments; and
transmitting the segments from the head end to users"" receivers, such that any one segment can simultaneously be sent to more than one receiver with no requirement at any time to dedicate the head end of the distribution system to any specific receivers.
According to a still further aspect of the present invention there is provided a receiver for receiving a program supplied to multiple users over a distribution system from a head end, said program being divided into a plurality of program segments, the receiver comprising:
a buffer storage means for storing a plurality of program segments transmitted from the head end of the distribution system; and
a processing means including means for calculating whether segments already held in said buffer storage means will be presented on the distribution system prior to playback and if so removing such segments from the buffer storage means whereby, in use, the program segments required for continuous playback of the program will always be available at the receiver.